1. Field of the Invention
The present invention relates to improvements in methods of identifying magnetic ink characters. More particularly, the present invention relates to identification of characters which are written in magnetic ink and read at high speed by check reader/sorters. This invention has particular application, but is not necessarily limited to characters which are printed in magnetic ink (referred to as Magnetic Ink Character Recognition, or MICR) in a standardized format or font such as the "E13B" font and are included spaced from the lower edge of bank checks, deposit slips and other documents. Such bank checks or other documents are typically processed on a machine such as an IBM Model 3694 document processor (also referred to as a check reader/sorter) at speeds of 200-1000 documents per minute and with approximately 250-1000 characters passing by a single magnetic read head each second.
2. Prior Art
Several different techniques have previously been used for reading MICR characters on checks and other documents at varying speeds. Some reading techniques are based upon multiple vertically-spaced magnetic reading heads, each head for reading a horizontal portion or slice of the each entire code line (or each character, in sequence.) Such character machines are generally (at least in relative terms) expensive because of the additional hardware and logic required to coordinate, correlate and interpret the readings of the multiple heads. Another technique is to read characters optically using an optical character recognition (OCR) apparatus, either by itself or in combination with a magnetic sensing apparatus.
Another technique for reading magnetic ink character includes a rather large single magnetic read head which spans the entire height of a magnetic ink character. A voltage proportional to the amount of flux change sensed by the reading head is generated as an indication of the character features in such single gap magnetic ink character readers. Such machines are generally easier to design and build and less expensive, but have the limitation of requiring sophisticated algorithms to determine the characters which have been read. These machines have the limitation that either the characters on some number of the documents are not read (identified) at all (a condition designated as a "reject" in the industry) or if read, generates an identification of a character other than the character which is printed. The improper identification is referred to in the industry as a "substitution". The banking industry has determined that both substitutions and rejects are undesirable, yet the number of checks and other MICR-coded documents handled each year is ever increasing, requiring more reliable equipment in the banking and similar channels.
While checks are preprinted with MICR bank routing and customer account numbers when blank checks are printed, the right portion of the MICR-line is left blank and reserved for the amount of the check. This amount field is typically added in a process called "inscribing" the amount field when the first bank receives the check. Various check inscribing machines are commercially available and in use today, each of which is somewhat different in the quality with which characters are formed on the check and in terms of spacing between features on the individual characters.
In some machines, the checks can have perfectly formed characters, but apparatus for moving the check past the magnetic read heads may not move the check at a uniform rate, making the code line difficult to read.
A concept of "re-timing" or adjusting recognition logic for variations in speed of transport or printing variations is known in single gap magnetic reading systems of the prior art. All such known systems, however, make adjustments on the fly, or in real time, based upon the past history and not in response to a total character. Such systems, which are disclosed in U.S. Pat. Nos. 3,316,536; 3,528,058; and 4,356,472; can not adjust for isolated variations, and therefore can lead to errors in the reading of magnetic ink characters.
The magnetic ink character recognition systems in use today have the additional disadvantage that a small ink spot in certain regions of the character prevent the reading of the character, even if the remainder of the character is perfectly legible. This occurs, in part, because some machines assume that the first peak detected must normalize the reading for the entire character. While that system may work well when the first peak of a read character is a part of a real character, the reading of an ink spot as the first character "portion" ruins the system, leading to either a reject or a substitution in many cases, both of which are undesirable.
Yet another method of identifying characters simply identifies character peaks, either ignoring their location completely or assuming that the peaks occur at regular time intervals after an opening peak. U.S. Pat. Nos. 3,851,309 and 4,143,355 are illustrative of this technique. However, this technique is not reliable in the identification of characters, because the timing of the peaks is important to the proper recognition of characters (e.g., to determine whether a character is a "2" or a "5", the timing between the peaks is the significant factor.)
U.S. Pat. No. 2,995,727 illustrates a system for comparing signals to determine their similarity in a complex amplitude versus time arrangement such as speech and character recognition. U.S. Pat. No. 3,605,092 detects MICR characters while avoiding misstarts by looking at the slope of the MICR wave form to determine whether a peak is present. U.S. Pat. No. 4,148,010 reads magnetic ink characters with the timing set from the center of gravity of the sensed peaks.
U.S. Pat. No. 4,245,211 includes a method of adjusting the system timing to align the character feature changes with the intervals; it employs a phased locked loop response to the detected peaks to accomplish this.
Other limitations and disadvantages are well known to those skilled in the art of reading magnetic ink characters and processing the information obtained by magnetic reading heads.